Cathode heater



July 16, 1968 E. R. SANDERS 3,393,342

CATHODE HEATER Filed March 14, 1946 FIG. 2

INVENTOR E DWI/V R. SANDERS BY (Q@7@2WJ Q/Z WQRNEY United States Patent Office 3,393,342 Patented July 16, 1968 3,393,342 .CATHODE HEATER Edwin R. Sanders, Silver Spring, Md., assignor to the ,Uniterl States of America asrepresented by the Secretary of the Navy v Filed Mar. 14, 1946, S er.' No. 654,500

Claims. (Cl; 313346) This invention relates to arrangements for heating a cathode of an electronic tube. The object of the invention is to provide an improved cathode heater suitable for use in a proximity fuze or in other applications requiring a minimum consumption of A battery energy or precluding the use of such a battery. A proximity fuze is a prior-art device for detonating a projectile or rocket. Such a fuze includes one or ,more electronic tubes but must be light in weight and compact. Since the tube potential sources must also be light and compact, current drains thereon must be reduced to a minimum.

It is immaterial how the cathode of a tube is heated, provided only that it is brought to a proper temperature to produce a substantial emission of electrons. A heater in accordance with the present invention produces the required heat by chemical reaction.

As a high temperature is required, this chemical reaction is of the type usually designated as rapid combustion in which much energy is liberated in a relatively short time with a resultant high temperature. That of the thermit type is particularly suitable. It consists in general of the reaction between a finely divided metal such as aluminum, magnesium and the like, and an oxide of a metal of high melting point, such as iron or chromium. The light metal combines readily with the oxygen in the heavy metal oxide, reducing the heavy metal and itself becoming an oxide generating suflicient heat to melt the reduced metal of high melting point. A

While one feature of the invention resides broadly in the use of such chemical means to heat a cathode, other features relate to physical characteristics of a cathode which is especially well adapted to utilize such method of heating.

It is found that the reduced metal and/ or slag produced by the reaction occupy less space than the original charge. In the present embodiment, the preferred shape of the cathode is that of the bottom or end of a cylinder which contains the charge before and after the reaction. In order to keep the hot material in close contact with the bottom of the cylinder, a piston or plunger is provided. This piston is made of refractory heat-insulating material, for example asbestos, and is urged toward the bottom of the cylinder by a spring or the like.

Preferably also there is a rigid post within the spring to act as a stop or abutment for the piston.

Other objects and many of the attendant advantages of this invention will become evident from the following detailed description when taken in conjunction with the accompanying drawing, wherein:

FIG. 1 shows a section of an electron tube having a chemically heated cathode embodying the invention in a. particular form; and

FIG. 2 shows a fragmentary section of a slightly modified form of heater construction.

Referring first to FIG. 1 there is illustrated a container 1 preferably of refractory metal having a bottom 2 which constitutes the electron emitting surface. This bottom 2 is made of tungsten or the like or it may be made of refractory metal such as a nickel or platinum alloy having a coating of a mixture of barium and strontium oxides or other suitable emitter, as preferred in any particular case.

This surface 2 serves as the cathode or electron emitter of the thermionic tube here shown as an oscillator in a proximity fuze circuit. There is a coil 5-6 tapped at 7, 17- representing a conductor electrically returning to the cathode 2, the coil portion 5 serving as the grid coil and the coil portion 6 as the plate coil of a Hartley type oscillator. A condenser 23 isolates the grid from the plate with respect to the DC. power supply, and a, resistor 24 serves as the grid leak.

, Inasmuch as the only essential in producing the emission of electrons is the production of sufficient heat, this is accomplished here without the expenditure of electrical energy by substituting chemical heating means.

The numeral 9 indicates a reaction mixture enclosed in the container 1 and in contact with the cathode portion 2 of said container. While a thermit type of material is preferred, it will be understood that the invention is not necessarily limited to such specific chemicals, and that any chemical charge, which contains proper ingredients for self-combustion and which does not produce an undesirably rapid emission of gases which might rupture the container, may be used as a filling for the container 1.

While it is immaterial to the electrical operation of the electronic tube how the reaction is initiated, a specific means is here illustrated. It comprises an ignition resistor, shown as a wire 10 attached to terminals 15 and 16 through an asbestos plug or plunger 11. The plunger acts as a piston with respect to the cylinder 1, although it need not make gas-tight contact therein. Upon supplying electricity to the terminals 15 and 16, the wire 10, due to its electrical resistance, is heated to incandescence in order to ignite the charge 9. In order to economize electrical energy, supplied from a battery or cell 21, through the wires 18, 20 and 22, a protective device in the nature of a fuse wire 19 is placed in series with the igniter wire 10. This wire 19, which enters the chamber in container 1 through the small insulators 25 is embedded in the combustible mixture 9 and destroyed by the combustion, either by burning up or by melting away. Its destruction automatically opens the circuit as soon as the composition 9 has been burned.

One application is to employ a thermionic device of this type within a projectile. Certain peculiarities of design are necessary to enable it to withstand the severe stresses produced when the projectile is fired. For example, a setback stud or lug 13, in the form of a solid post, normally bears against the outer surface of the refractory plug 11 to take the setback forces. 14 represents an internal surface of the shell against which the post 13 abuts.

The reaction mixture 9 usually decreases in volume when thce reaction is in progress and therefore the plug 11 is designed to follow the mixture into the container 1 and maintain it compressed against the cathode surface 2 in proper heat-conveying relationship thereto. If this plug 11, or equivalent, were not provided, another action that occurs in a rapidly spinning projectile would militate against efficient heating of the cathode surface 2: the centrifugal force would cause the products of the reaction to be thrown against the cylinder wall of the container 1 instead of against its bottom 2 so that the cathode would not be heated eificiently. The spring 12 surrounding the post 13 and bearing against the asbestos plug effectively prevents this undesirable centrifugal action from moving the material away from the cathode surface 2.

The operation of the present invention is summarized briefly as follows:

Upon firing of the projectile, an electrical impulse is simultaneously given in any desired way, not forming a part of the present invention, to the terminals 15 and 16, thereby causing the wire 10 to become heated sufliciently to ignite the charge 9 and resulting in the production of extremely hot products, such as slag and/0r reduced metal or the like, within the container 1. The heat of this mixture rapidly brings the cathode to the proper operating temperature and the combustion products themselves are maintained in good heating relation with said cathode by means of the refractory plug 11, which is pressed toward the surface 2 by the spring 12.

An incidental effect of the motion of plug 11 is that in its travel into the container 1 this plug will positively remove that portion of conductor 19 within said container. Occasionally said conductor may remain electrically continuous even though molten, because it is supported by the reaction mixture. The plug 11 thus assures positive interruption of the circuit by bodily removing the said conductor, and constitutes an additional safety device that protects the battery 21 from premature exhaustion.

While an electrical ignition means has been described in connection with FIG. 1, other igniting devices may also be used if desired. In FIG. 2 there is shown a percussion igniter consisting of a cap 25 containing a fulminate of mercury, lead azide or other percussion material 26, and a pin 27 attached to the plug 11 so that when the shell is fired the pin is driven by setback into the cap 25 so as to ignite the composition 26 and this in turn ignites the composition 9.

While there have been shown what are at present considered to be the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the true scope of the invention claimed hereinafter.

What is claimed is:

1. In combination with an electron discharge device having an evacuated envelope, and an electrode in the envelope, a container carried by the envelope and projecting thereinto to form a portion of the wall of said envelope, an element associated with the container and acting as an electron emitter when heated, a chemical reaction mixture carried by the container in heat exchanging relation with said element, an igniter including an electrically'heatable resistor in contact with said mixture for initiating said reaction and thereby heating said element to emitting temperature, and an electrical conductor in series with said igniter and in heat-exchanging relationship with said mixture to be destroyed by the heat and thus interrupt the heating circuit when the reaction mixture has become ignited, said reaction mixture being maintained out of contact with said emitter element and electrode by said container.

2. The combination recited in claim 1, wherein the electrical conductor is a fusible Wire embedded in the reaction mixture.

3. In combination with an electron discharge device having an evacuated envelope, and an electrode in the envelope, a container carried by the envelope and projecting thereinto to form a portion of the wall of said envelope, an element associated with the container and acting as an electron emitter when heated, a chemical reaction mixture carried by the container in heat exchanging relation with said element, an igniter including an electrically heatable resistor in contact with said mixture for initiating said reaction and thereby heating said element to emitting temperature, an electrical conductor 4v in series with said igniter, a plunger movable within said container, and a spring urging said plunger into the container, whereby said plunger will break the conductor and thus interrupt the heating dircuit when the reaction mixture has decreased in volume upon burning, said reaction mixture being maintained out of contact with said emitter element and electrode by .said container while being maintained in heat exchanging relation with said emitter element as said reaction mixture decreases in volume.

4. In combination with an electron discharge device having an evacuated envelope, and an electrode in the envelope, a container carried by the envelope and projecting thereinto to form a portion of the wall of said envelope, an element associated with the container and acting as an electron emitter when heated, a chemical reaction mixture carried by the container in heat exchanging relation with said element, an igniter including an electrically heatable resistor in contact with said mixture for initiating said reaction and thereby heating said element to emitting temperature, an electrical conductor in series with said igniter and in heat-exchanging relationship with said mixture to be destroyed by the heat and thus interrupt the heating circuit when the reaction mixture has become ignited, and additional means comprising a spring-actuated plunger for mechanically breaking said conductor to provide an auxiliary device to assure breaking the circuit, should the conductor fail to break by melting, said reaction mixture being maintained out of contact with said emitter element and electrode by said container while being maintained in heat exchanging relation with said emitter element as said reaction mixture decreases in volume.

5. In combination with an electron discharge device having an evacuated envelope, and an electrode in the envelope, a container carried by the envelope and projecting thereinto to form a portion of the wall of said envelope, an element associated with the container and acting as an electron emitter when heated, a chemical reaction mixture carried by the container and in heat exchanging relation with said emitter element, means in contact with said mixture for initiating said reaction whereby said coated element is heated to emitting temperature, said reaction mixture being maintained out of contact with said emitter element by said container, and means carried in said container for keeping said reaction mixture in heat exchanging relation with said emitter element while a reaction is taking place in said container.

References Cited UNITED STATES PATENTS 790,401 5/ 1905 Semple 102-78 1,368,584 2/1921 Torrisi 250-27.5 1,673,850 6/1928 Tietig 250--27.5 2,424,526 7/ 1947 White 313-270 JOHN W. HUCKERT, Primary Examiner.

G. W. STRACHAN, JAMES L. BREWNNIK, WILLIAM WILES, Examiners.

A. J. JAMES, Assistant Examiner. 

1. IN A COMBINATION WITH AN ELECTRON DISCHARGE DEVICE HAVING AN EVACUATED ENVELOPE, AND AN ELECTRODE IN THE ENVELOPE, A CONTAINER CARRIED BY THE ENVELOPE AND PROJECTING THEREINTO TO FORM A PORTION OF THE WALL OF SAID ENVELOPE, AN ELEMENT ASSOCIATED WITH THE CONTAINER AND ACTING AS AN ELECTRON EMITTER WHEN HEATED, A CHEMICAL REACTION MIXTURE CARRIED BY THE CONTAINER IN HEAT EXCHANGING RELATION WITH SAID ELEMENT, AN IGNITER INCLUDING AN ELECTRICALLY HEATABLE RESISTOR IN CONTACT WITH SAID MIXTURE FOR INITIATING SAID REACTION AND THEREBY HEATING SAID ELEMENT TO EMITTING TEMPERATURE, AND AN ELECTRICAL CONDUCTOR IN SERIES WITH SAID IGNITER AND IN HEAT-EXCHANGING RELATIONSHIP WITH SAID MIXTURE TO BE DESTROYED BY THE HEAT AND THUS INTERRUPT THE HEATING CIRCUIT WHEN THE REACTION MIXTURE HAS BECOME IGNITED, SAID REACTION MIXTURE BEING MAIN- 